2003年夏季淮河流域梅雨期西太平洋副高结构和活动特征及动力机制分析

The Structure and Activity Characteristics of the Western Pacific Subtropical Anticyclone and Its Dynamical Mechanism During the Meiyu Period over the Huaihe River Basin in 2003

通过资料分析和诊断, 揭示了在2003年6～7月淮河流域暴雨期间, 西太平洋副高相对偏北并且呈现南北变化相对稳定、东西变化明显的特征; 强劲而稳定少动的中纬度西风急流使得西太平洋副高难以北抬, 从而造成了淮河流域降雨带的稳定少动. 同时, 分析表明每一次雨锋的出现伴有高层南亚高压的东伸, 并诱发500 hPa西太平洋副高西伸至我国沿海, 导致淮河流域多雨, 江南干旱高温.分析还发现高、低空副热带高压影响天气系统发展的如下机制: (1) 沿30°N东伸的高层南亚高压脊在东部30°N以北地区引起辐散和上升, 在30°N以南地区引起辐合和下沉; (2) 江南高层的辐合下沉气流在中低空的辐散增强了局地的负涡度, 诱发西太平洋副高西伸; (3) 沿增强了的西太平洋副高西北侧的偏西南气流在30°N以北辐合, 增强了局地的上升运动, 为暴雨的产生创造了大尺度的背景流场; (4) 副高西北侧的暴雨加强了低空的南风和高层的北风, 从而使高层东伸的南亚高压和低层西伸的西太平洋副高在我国东部稳定维持.

The routine NCEP/NCAR reanalysis data were used for analyzing the characteristics of the western Pacific subtropical anticyclone （WPSA） during the Meiyu period in 2003. It is found that the WPSA is characterized by northward and stable relative to that of the climate mean, as well as the obvious east-west oscillation. The northward moving of the WPSA is prevented by the strong and stable western jet in mid-latitudes, thus causes the stable rainband over the Huaihe River basin. Meanwhile, the results show that the occurrence of each torrential rain is almost accompanied by the eastward moving of the South Asia high in upper-layer, and the westward extension of the 500 hPa WPSA to west coast of China. As a result, the high temperature and drought occur over the south of the Yangtze River. The possible mechanisms of the subtropical anticyclone in the higher and lower layer triggering the development of the weather system are summarized as follows： （1） The ridge of the eastward South Asia high along 30°N causes the divergence and ascent motion to the north of 30°N while the convergence and descending motion to the south of 30°N over the Huaihe River basin. （2） The divergence of the convergence and descending airflow further enhances the local negative vorticity in the lower layer, which leads to the westward extending of the WPSA. （3） The convergence of the southwesterly to the north of 30°N along the northwest of the WPSA strengthens the local ascending motion, which provides a large-scale background favorable for the torrential rain. （4） The torrential rain to the northwest of the WPSA intensifies the southerly in the lower layer and the northerly in the higher layer, and it makes the eastward South Asia high and the WPSA stably maintain over the area.